The present invention relates to generally to a suspension system for tilting vehicles. More specifically, the present invention relates to an active suspension for a tilting vehicle that expands upon the four-bar principal by extending the lower suspension linkage to create a large storage platform that allows heavy objects, such as battery banks, to be installed into the vehicle while preserving a lowered center of gravity.
Currently, most of the motor vehicles that are on the highways are four-wheeled vehicles that tend to be larger, heavier and, as a result less, fuel-efficient than three-wheeled motor vehicles. Despite the fact that four-wheeled vehicles can be seen to enjoy more widespread use and acceptance, there are several advantages that are provided by modern three-wheeled vehicles. For example, under most circumstances three-wheel vehicles are, by their nature, more stable than four-wheel vehicles due to the fact that three contact points will form a plane under all circumstances, whereas four contact points will not. Another advantage is that three-wheel vehicles afford a nearly ideal wheel loading distribution for maximum tire traction in both acceleration and braking situations. Despite the advantages that three-wheeled vehicles enjoy over four-wheel vehicles, the main drawback of a three-wheel vehicle is that during a turn, rather than having two outside wheels in contact with the road surface, the three-wheeled vehicle only has a single outside wheel that must bear the entire centrifugal load generated by the vehicle while negotiating the turn. In this regard, the centrifugal force tends to overload the outside tire causing the vehicle to slip out of the direction of the turn unless some additional means of force compensation is provided. Further, the three-wheeled vehicle geometry allows the force vector associated with the vehicle's center of gravity to quickly fall outside the wheelbase of the vehicle causing an unstable condition and increasing the possibility of overturning the vehicle. To make this condition worse, as the center of gravity of the vehicle (including an operator and any load being carried by the vehicle) raises higher, the potential for vehicle instability and overturning becomes much greater. In order to counteract these forces, generally three-wheeled vehicles often employ a tilting and banking mechanism that shifts the vehicle's center of gravity toward the inside as it negotiates a turn thereby keeping more of the centrifugal load over the inside tire.
One prior art approach used in solving this problem was to utilize a pair of small spaced-apart wheels with a tilting frame. In this arrangement, the wheels remained substantially vertically inclined while only the vehicle frame leaned into turns. The problem is that such a construction is somewhat self-defeating in that it lacks the ability to tilt and bank in a manner that directs the traction forces through the center of gravity of the vehicle and the point of contact of the vehicle wheels with the ground. Alternatively, hydraulic cylinder load-leveling systems have been devised, however, these systems quickly become complex and require a fair amount of electronics and computing power to generate sufficient control in order to obtain optimal response.
The ability to overcome the aforementioned handling problems in three-wheeled vehicles becomes even more important as more emphasis is placed upon alternative fuel and/or hybrid vehicles. While the improved efficiencies typically realized by three-wheeled frame geometries would be highly advantageous in connection with alternative fuel systems, often such systems require large battery banks to store sufficient battery capacity to produce a useful range. Further, the chemistry of these batteries requires that they employ some form of heavy metal therein. As the size of the batteries and the number of batteries in a given battery bank increases, the weight that is required to be carried within the vehicle also greatly increases. The problem is further aggravated by that fact that most prior art solutions provided for installing these batteries in a vertical location somewhere beneath the vehicle seat. Further, all of these solutions place the batteries in a vertical stacked arrangement that places their significant weight relatively high in the vehicle platform. As a result, such battery placement greatly raises the height of the vehicle's center of gravity thereby adding to the stability issues raised above.
Accordingly, there is a need for a suspension system for a tilting vehicle that allows the forces generated by the vehicle to be transferred using a center of effort that is directed perpendicular to the traction surfaces of the tires. Further, there is a need for a suspension system for a tilting vehicle that provides a storage position at the lowest possible position within the vehicle for storage of heavy items such as large battery banks. Finally, there is a need for a suspension system for a tilting vehicle that both facilitates a low center of gravity arrangement by placing heavy load storage in a lowered position while also still allowing active tilt control by the vehicle operator in a manner that greatly reduces the complexity of the system and the need for multiple sensors, hydraulic arrays and substantial computer power.